Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755797AbdCGPj4 (ORCPT ); Tue, 7 Mar 2017 10:39:56 -0500 Received: from mail-sn1nam02on0130.outbound.protection.outlook.com ([104.47.36.130]:48083 "EHLO NAM02-SN1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755432AbdCGPj2 (ORCPT ); Tue, 7 Mar 2017 10:39:28 -0500 Authentication-Results: hpe.com; dkim=none (message not signed) header.d=none;hpe.com; dmarc=none action=none header.from=hpe.com; Subject: Re: [PATCH 1/2] x86/platform: Add a low priority low frequency NMI call chain To: Ingo Molnar References: <20170306181737.059578494@asylum.americas.sgi.com> <20170306181737.322206440@asylum.americas.sgi.com> <20170307074210.GA24782@gmail.com> CC: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Don Zickus , Peter Zijlstra , Dimitri Sivanich , Frank Ramsay , Russ Anderson , Tony Ernst , , From: Mike Travis Message-ID: Date: Tue, 7 Mar 2017 07:38:39 -0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20170307074210.GA24782@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [73.222.225.80] X-ClientProxiedBy: BN3PR09CA0055.namprd09.prod.outlook.com (10.174.65.151) To AT5PR84MB0228.NAMPRD84.PROD.OUTLOOK.COM (10.162.138.153) X-MS-Office365-Filtering-Correlation-Id: 93e1c8e7-0fc9-438c-5368-08d4657015ef X-MS-Office365-Filtering-HT: Tenant X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001)(48565401081);SRVR:AT5PR84MB0228; X-Microsoft-Exchange-Diagnostics: 1;AT5PR84MB0228;3:Z3j9Zzk4cfMSBqq7JMLNRKo6rLHSx0HgnZ+HFNQaXYM9p0vNM0F2u8LfnS6qcfHAG3oeJM4P3B2YUzoNlana0rOGuWoyVNN0vgMmSL6jm3mLRLPqA8qroCZhWOwpVdhw7KedFtTLrAmuj0YjJwpiFhzAT77QIC1WAnhzukZLRI01jbip7tqY3GO+kY4yChvO4rF/+ceIF3pr/vpy11itVDkMYddq4Oyilc3Yk55MjDW6TNt92JBGB87d0FczEqDpwR3/SFaC1TGR5cP8BAUNxDkI3vjZ80YdXyltlYnPAHA=;25:GpHIfeX07l6VIRjwBZups00h3+GWLwSfDkZNHQ688LF0ytc9+3SeE0/B6XTnqV3XB7sN8J6Kyo55OuHyNdq3dAujO9i8gjugKU+Nylw9TY5GQpVTCETYmqKpaXOx6gxAcmC9DL5ynbsK/MwHW0Mu7IfnSAnmBfBNSWWgETI+5rQuHqzHYaDsK1iyZHgxgSj2j8aRx/c3weCnKYnjxUvlbFYADNXr4d0RahEZdA4kIXt3XPZ1egxK0Vbzn6+tZUs54IE9UoBnvjn47g22v4Mam5JaQQFRxA9NNxIeDMKw9GbXgtWLrYwHSmTM3+IR6+sOci95LDYJs1SHZdFvYOUJX8tsl2XHdbg/QYjsT4WOiBR9Izr2gf3Ma+Z8abR782R2JfRfteVao4k1SZKuverObXx7f7irH9KiH0T3YsoFkRvD77BiRj1YTwNkl0Idm4+kED8EykMOjeIaiPDVBXtvyw== X-Microsoft-Exchange-Diagnostics: 1;AT5PR84MB0228;31:WV4/JWCg6YjkJ1jDe+EwjKjt7WddHaltZOFlNk3JV8bBwMvfhxAHoUz/t2SEfU5qeJeP5sd6ZJftiYl79xNp+MZiaZBfc8a0JnBl2R9YkKbA23K/wo8zynXSiVpSyBBuLGiDoUVUryhq8FzbV/G/+ckh22wZCI6YmWiOc+HusuW6w8cdy0Nltx0pteyX1/vxg/d+jTOsUmBr0dudSqZAFatOCjNLzOhUjznebgTpaLODNILo1FkSeiy+J67SRj4U;20: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 X-Microsoft-Antispam-PRVS: X-Exchange-Antispam-Report-Test: UriScan:(227479698468861)(211171220733660); 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This mimics the current >> NMI_UNKNOWN call chain except it eliminates the WARNING message about >> multiple NMI handlers registering on this call chain. >> >> This call chain dramatically lowers the NMI call frequency when high >> frequency NMI tools are in use, notably the perf tools. It is required >> for NMI handlers that cannot sustain a high NMI call rate without >> ramifications to the system operability. > > So how about we just turn off that warning instead? I don't remember the last time > it actually _helped_ us find any kernel or hardware bug - and it has caused tons > of problems... I can do that, with an even simpler patch... > > It's not like we warn about excess regular IRQs either - we either handle them or > at most increase a counter somewhere. We could do the same for NMIs: introduce a > counter somewhere that counts the number of seemingly unhandled NMIs. Really "unknown" NMI errors are reported by either the "dazed and confused" message or if the panic on unknown nmi is set, then the system will panic. So unknown NMI occurrences are already being dealt with. Plus the following stats are being collected, though I'm not sure of any reporting facility: struct nmi_stats { unsigned int normal; unsigned int unknown; unsigned int external; unsigned int swallow; }; static DEFINE_PER_CPU(struct nmi_stats, nmi_stats); > > But in any case, we should not spam the kernel log, neither with high, nor with > low frequency. > > Thanks, > > Ingo >